binutils-gdb/bfd/syms.c

/* Generic symbol-table support for the BFD library.
   Copyright (C) 1990-1991 Free Software Foundation, Inc.
   Written by Cygnus Support.

This file is part of BFD, the Binary File Descriptor library.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */

/*
SECTION
	Symbols

DESCRIPTION
	BFD trys to maintain as much symbol information as it can when
	it moves information from file to file. BFD passes information
	to applications though the <<asymbol>> structure. When the
	applicationrequests the symbol table, BFD reads the table in
	the native form and translates parts of it into the internal
	format. To maintain more than the infomation passed to
	applications some targets keep some information 'behind the
	sceans', in a structure only the particular back end knows
	about. For example, the coff back end keeps the original
	symbol table structure as well as the canonical structure when
	a BFD is read in. On output, the coff back end can reconstruct
	the output symbol table so that no information is lost, even
	information unique to coff which BFD doesn't know or
	understand. If a coff symbol table was read, but was written
	through an a.out back end, all the coff specific information
	would be lost. (.. until BFD 2 :).  The symbol table of a BFD
	is not necessarily read in until a canonicalize request is
	made. Then the BFD back end fills in a table provided by the
	application with pointers to the canonical information.  To
	output symbols, the application provides BFD with a table of
	pointers to pointers to <<asymbol>>s. This allows applications
	like the linker to output a symbol as read, since the 'behind
	the sceens' information will be still available. 
@menu
* Reading Symbols::
* Writing Symbols::
* typedef asymbol::
* symbol handling functions::
@end menu

@node Reading Symbols, Writing Symbols, Symbols, Symbols
SUBSECTION
	Reading Symbols

DESCRIPTION
	There are two stages to reading a symbol table from a BFD;
	allocating storage, and the actual reading process. This is an
	excerpt from an appliction which reads the symbol table:

EXAMPLE

  unsigned int storage_needed;
  asymbol **symbol_table;
  unsigned int number_of_symbols;
  unsigned int i;

  storage_needed = get_symtab_upper_bound (abfd);

  if (storage_needed == 0) {
     return ;
  }
  symbol_table = (asymbol **) bfd_xmalloc (storage_needed);
    ...
  number_of_symbols = 
     bfd_canonicalize_symtab (abfd, symbol_table); 

  for (i = 0; i < number_of_symbols; i++) {
     process_symbol (symbol_table[i]);
  }

DESCRIPTION

	All storage for the symbols themselves is in an obstack
	connected to the BFD, and is freed when the BFD is closed.


@node Writing Symbols, typedef asymbol, Reading Symbols, Symbols
SUBSECTION
	Writing Symbols

DESCRIPTION
	Writing of a symbol table is automatic when a BFD open for
	writing is closed. The application attaches a vector of
	pointers to pointers to symbols to the BFD being written, and
	fills in the symbol count. The close and cleanup code reads
	through the table provided and performs all the necessary
	operations. The outputing code must always be provided with an
	'owned' symbol; one which has come from another BFD, or one
	which has been created using <<bfd_make_empty_symbol>>.   An
	example showing the creation of a symbol table with only one element:

EXAMPLE
#include "bfd.h"
main() 
{
  bfd *abfd;
  asymbol *ptrs[2];
  asymbol *new;

  abfd = bfd_openw("foo","a.out-sunos-big");
  bfd_set_format(abfd, bfd_object);
  new = bfd_make_empty_symbol(abfd);
  new->name = "dummy_symbol";
  new->section = (asection *)0;
  new->flags = BSF_ABSOLUTE | BSF_GLOBAL;
  new->value = 0x12345;

  ptrs[0] = new;
  ptrs[1] = (asymbol *)0;
  
  bfd_set_symtab(abfd, ptrs, 1);
  bfd_close(abfd);
}

./makesym 
nm foo
00012345 A dummy_symbol


DESCRIPTION
	Many formats cannot represent arbitary symbol information; for
 	instance the <<a.out>> object format does not allow an
	arbitary number of sections. A symbol pointing to a section
	which is not one  of <<.text>>, <<.data>> or <<.bss>> cannot
	be described. 

*/


/*doc*
@node typedef asymbol, symbol handling functions, Writing Symbols, Symbols

*/
/*
TYPEDEF
	typedef asymbol

DESCRIPTION
	An <<asymbol>> has the form:

.typedef struct symbol_cache_entry 
.{
	A pointer to the BFD which owns the symbol. This information
	is necessary so that a back end can work out what additional
	(invisible to the application writer) information is carried
	with the symbol. 

.  struct _bfd *the_bfd;

The text of the symbol. The name is left alone, and not copied - the
application may not alter it. 

.   CONST char *name;

The value of the symbol.

.   symvalue value;

Attributes of a symbol:

.#define BSF_NO_FLAGS    0x00

The symbol has local scope; <<static>> in <<C>>. The value is
the offset into the section of the data.

.#define BSF_LOCAL	0x01

The symbol has global scope; initialized data in <<C>>. The value
is the offset into the section of the data.

.#define BSF_GLOBAL	0x02

Obsolete

.#define BSF_IMPORT	0x04

The symbol has global scope, and is exported. The value is the offset
into the section of the data.

.#define BSF_EXPORT	0x08

The symbol is undefined. <<extern>> in <<C>>. The value has no meaning.

.#define BSF_UNDEFINED	0x10	

The symbol is common, initialized to zero; default in <<C>>. The
value is the size of the object in bytes.

.#define BSF_FORT_COMM	0x20	

A normal <<C>> symbol would be one of:
<<BSF_LOCAL>>, <<BSF_FORT_COMM>>,  <<BSF_UNDEFINED>> or <<BSF_EXPORT|BSD_GLOBAL>>

The symbol is a debugging record. The value has an arbitary meaning.

.#define BSF_DEBUGGING	0x40

The symbol has no section attached, any value is the actual value and
is not a relative offset to a section.

.#define BSF_ABSOLUTE	0x80

Used by the linker

.#define BSF_KEEP        0x10000
.#define BSF_KEEP_G      0x80000

Unused

.#define BSF_WEAK        0x100000
.#define BSF_CTOR        0x200000 
.#define BSF_FAKE        0x400000 

The symbol used to be a common symbol, but now it is allocated.

.#define BSF_OLD_COMMON  0x800000  

The default value for common data.

.#define BFD_FORT_COMM_DEFAULT_VALUE 0

In some files the type of a symbol sometimes alters its location
in an output file - ie in coff a <<ISFCN>> symbol which is also <<C_EXT>>
symbol appears where it was declared and not at the end of a section. 
This bit is set by the target BFD part to convey this information. 

.#define BSF_NOT_AT_END    0x40000

Signal that the symbol is the label of constructor section.

.#define BSF_CONSTRUCTOR   0x1000000

Signal that the symbol is a warning symbol. If the symbol is a warning
symbol, then the value field (I know this is tacky) will point to the
asymbol which when referenced will cause the warning.

.#define BSF_WARNING       0x2000000

Signal that the symbol is indirect. The value of the symbol is a
pointer to an undefined asymbol which contains the name to use
instead.

.#define BSF_INDIRECT     0x4000000

.  flagword flags;

A pointer to the section to which this symbol is relative, or 0 if the
symbol is absolute or undefined. Note that it is not sufficient to set
this location to 0 to mark a symbol as absolute - the flag
<<BSF_ABSOLUTE>> must be set also.

.  struct sec *section;

Back end special data. This is being phased out in favour of making
this a union.

.  PTR udata;	
.} asymbol;

*/

#include "bfd.h"
#include "sysdep.h"
#include "libbfd.h"
#include "stab.gnu.h"
 
/*
@node symbol handling functions,  , typedef asymbol, Symbols
SUBSECTION
	Symbol Handling Functions

*/

/*
FUNCTION
	get_symtab_upper_bound

DESCRIPTION
	Returns the number of bytes required in a vector of pointers
	to <<asymbols>> for all the symbols in the supplied BFD,
	including a terminal NULL pointer. If there are no symbols in
	the BFD, then 0 is returned.

.#define get_symtab_upper_bound(abfd) \
.     BFD_SEND (abfd, _get_symtab_upper_bound, (abfd))

*/

/*
FUNCTION
	bfd_canonicalize_symtab

DESCRIPTION
	Supplied a BFD and a pointer to an uninitialized vector of
	pointers. This reads in the symbols from the BFD, and fills in
	the table with pointers to the symbols, and a trailing NULL.
	The routine returns the actual number of symbol pointers not
	including the NULL.


.#define bfd_canonicalize_symtab(abfd, location) \
.     BFD_SEND (abfd, _bfd_canonicalize_symtab,\
.                  (abfd, location))

*/


/*
FUNCTION
	bfd_set_symtab

DESCRIPTION
	Provided a table of pointers to symbols and a count, writes to
	the output BFD the symbols when closed.

SYNOPSIS
	boolean bfd_set_symtab (bfd *, asymbol **, unsigned int );
*/

boolean
bfd_set_symtab (abfd, location, symcount)
     bfd *abfd;
     asymbol **location;
     unsigned int symcount;
{
  if ((abfd->format != bfd_object) || (bfd_read_p (abfd))) {
    bfd_error = invalid_operation;
    return false;
  }

  bfd_get_outsymbols (abfd) = location;
  bfd_get_symcount (abfd) = symcount;
  return true;
}

/*
FUNCTION
	bfd_print_symbol_vandf

DESCRIPTION
	Prints the value and flags of the symbol supplied to the stream file.

SYNOPSIS
	void bfd_print_symbol_vandf(PTR file, asymbol *symbol);
*/
void
DEFUN(bfd_print_symbol_vandf,(file, symbol),
PTR file AND
asymbol *symbol)
{
  flagword type = symbol->flags;
  if (symbol->section != (asection *)NULL)
      {
	fprintf_vma(file, symbol->value+symbol->section->vma);
      }
  else 
      {
	fprintf_vma(file, symbol->value);
      }
  fprintf(file," %c%c%c%c%c%c%c%c%c%c",
	  (type & BSF_LOCAL)  ? 'l':' ',
	  (type & BSF_GLOBAL) ? 'g' : ' ',
	  (type & BSF_IMPORT) ? 'i' : ' ',
	  (type & BSF_EXPORT) ? 'e' : ' ',
	  (type & BSF_UNDEFINED) ? 'u' : ' ',
	  (type & BSF_FORT_COMM) ? 'c' : ' ',
	  (type & BSF_CONSTRUCTOR) ? 'C' : ' ',
	  (type & BSF_WARNING) ? 'W' : ' ',
	  (type & BSF_INDIRECT) ? 'I' : ' ',
	  (type & BSF_DEBUGGING) ? 'd' :' ');

}


/*
FUNCTION
	bfd_make_empty_symbol

DESCRIPTION
	This function creates a new <<asymbol>> structure for the BFD,
	and returns a pointer to it.

	This routine is necessary, since each back end has private
	information surrounding the <<asymbol>>. Building your own
	<<asymbol>> and pointing to it will not create the private
	information, and will cause problems later on.

.#define bfd_make_empty_symbol(abfd) \
.     BFD_SEND (abfd, _bfd_make_empty_symbol, (abfd))
*/

/*
FUNCTION
	bfd_decode_symclass

DESCRIPTION
	Return a lower-case character corresponding to the symbol
	class of symbol.

SYNOPSIS
	int bfd_decode_symclass(asymbol *symbol);
*/
int
DEFUN(bfd_decode_symclass,(symbol),
asymbol *symbol)
{
  flagword flags = symbol->flags;
  
  if (flags & BSF_FORT_COMM) return 'C';
  if (flags & BSF_UNDEFINED) return 'U';
  if (flags & BSF_ABSOLUTE)
       return (flags & BSF_GLOBAL) ? 'A' : 'a';
 
   if ( flags & (BSF_GLOBAL|BSF_LOCAL) ) {
     if (symbol->section == (asection *)NULL)
       return '*';
     else if ( !strcmp(symbol->section->name, ".text") )
       return (flags & BSF_GLOBAL) ? 'T' : 't';
     else if ( !strcmp(symbol->section->name, ".data") )
       return (flags & BSF_GLOBAL) ? 'D' : 'd';
     else if ( !strcmp(symbol->section->name, ".bss") )
       return (flags & BSF_GLOBAL) ? 'B' : 'b';
     else
       return (flags & BSF_GLOBAL) ? 'O' : 'o';
    }

  /* We don't have to handle these cases just yet, but we will soon:
     N_SETV: 'v'; 
     N_SETA: 'l'; 
     N_SETT: 'x';
     N_SETD: 'z';
     N_SETB: 's';
     N_INDR: 'i';
     */
 
  return '?';
}